'''SHA-1''' ('''S'''ecure '''H'''ash '''A'''lgorithm) is a cryptographic hash function that was first published in 1995 in Federal Information Processing Standards (FIPS) PUB 180-1 by the National Security Agency (NSA) as a fix to an unknown flaw found in SHA-0.

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In February of 2005 an attack was announced that could find collisions in SHA-1 requiring fewer than 2<sup>69</sup> operations.

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== Image types ==

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There are multiple types of Virtual Hard Disk (VHD) images:

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* Fixed-size hard disk image

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* Dynamic-size (or sparse) hard disk image

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* Differencing (or delta) hard disk image

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== Tools ==

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== External Links ==

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On most Unix systems the tool sha1sum can be used to compute the SHA-1 hash of a file or devices.